palladin

// Norvig's Spelling Corrector: http://norvig.com/spell-correct.html
open System.IO open System.Text.RegularExpressions

let edits1 (word : string) = 
    let splits = [for i in 0 .. word.Length do yield (word.[0..i-1], word.[i..])]
    let deletes = [for a, b in splits do if b <> "" then yield a + b.[1..]]
    let transposes = [for a, b in splits do if b.Length > 1 then yield a + string b.[1] + string b.[0] + b.[2..]]
    let replaces = [for a, b in splits do for c in 'a'..'z' do if b <> "" then yield a + string c + b.[1..]]
    let inserts = [for a, b in splits do for c in 'a'..'z' do yield a + string c + b]
    deletes @ transposes @ replaces @ inserts |> Set.ofList

palladin

let char c (s : string) = seq { if s.Length > 0 && s.[0] = c then yield s.Substring(1) }

let (=>) l r s = seq { for sl in l s do for sr in r sl -> sr }

let (<|>) l r s = seq { yield! l s; yield! r s }

let rec (<*>) e s = seq { yield s; yield! (e => (<*>) e) s }

let (<+>) e = e => (<*>) e

palladin

// Useful type aliases
type Actor = MailboxProcessor<obj>
type Ident = string
type Cond = Actor
type Env = Actor
 
 
let (<!>) (actor : Actor) (msg : 'T) = actor.Post msg
 
// run forever - template

palladin

// Functional Unparsing http://www.brics.dk/RS/98/12/BRICS-RS-98-12.pdf

open System
open System.Data
open System.Data.SqlClient


// Type Decls
type SqlText = string
type Counter = int

palladin

open System.Threading

type Atom<'T when 'T : not struct>(value : 'T) =
    let refCell = ref value
    
    let rec swap f = 
        let currentValue = !refCell
        let result = Interlocked.CompareExchange<'T>(refCell, f currentValue, currentValue)
        if obj.ReferenceEquals(result, currentValue) then ()
        else Thread.SpinWait 20; swap f

palladin

// Info: http://clojure.org/atoms

open System
open System.Threading

type Atom<'T when 'T : not struct>(value : 'T) =
    let refCell = ref value
    
    let rec swap f = 
        let currentValue = !refCell

palladin

// For more info
// http://www.springerlink.com/content/g74174vvl1861605/
// http://www.haskell.org/haskellwiki/Circular_programming

// Helper functions
let force (value : Lazy<_>) = value.Force()
let lazyMap f l = lazy (f (force l))

// Generic feedback loop function
let trace f input = 

palladin

// x = f(x) encoded in F#

let force (value : Lazy<_>) = value.Force()

let fix f = let rec x = lazy (f x) in x

// Examples
let fac = fix (fun f x -> if x = 0 then 1 else x * force f (x - 1) )
let nums = fix (fun v -> seq { yield 0; yield! Seq.map ((+) 1) (force v) }) 

palladin

let s : Printf.TextWriterFormat<_> = "let s : Printf.TextWriterFormat<_> = %c%s%c in
printf s (char 34) (s.Value) (char 34)" in printf s (char 34) (s.Value) (char 34)

palladin

// Haskell-inspired infinite sequences

#r "FSharp.Powerpack"

let rec repeat n = LazyList.consDelayed n (fun () -> repeat n)
repeat 1 // seq [1; 1; 1; 1; ...]

let rec integersFrom n = LazyList.consDelayed n (fun () -> LazyList.map ((+) 1) <| integersFrom n) 
integersFrom 3 // seq [3; 4; 5; 6; ...]